Implement SIP6

[braydonf]

Implements https://github.com/Storj/sips/blob/master/sip-0006.md

Part of: storj-archived/integration#5

[littleskunk]

Depricated and can be removed as well: https://github.com/braydonf/storj-lib/blob/sip6/.gitattributes

[littleskunk]

Lets say a renter uploads the same file with the same encrpytion to two bridges. At the end my farmer will store one shard with two contracts.

The current implementation will only look at the first contract and will ignore the second contract. The renter is not able to download his shard from the second bridge.

const nodeID = Object.keys(item.contracts)[0];
const contract = item.getContract({ nodeID: nodeID });
const bridgeExtendedKey = contract.get('renter_hd_key');
const bridge = self.farmerInterface.bridges.get(bridgeExtendedKey);
if (!bridge) {
  return res.send(500, { result: 'Not connected to bridge'});
}

[braydonf]

Used this instead:

const contract = item.getContract({ nodeID: contact.nodeID }); 

May need to use the hdKey instead, we'll see.

[braydonf]

Actually, looks like we can just use this:

const contract = item.getContract(contact);